A man from India said that he thought he knew the problem with last week's Tucson 2 conference, Towards a Science of Consciousness. The delegates and speakers, he said, came from far too narrow a range of concerns.

But for most others, the array of engineers, mathematicians, physicists, computer scientists, musicians, philosophers, linguists, neuroscientists, psychologists, clinicians and ill-defined freelance scholars among the 1,500-strong crowd was probably adequate.

During the week, they could feast upon quantum mechanics, the workings of human vision, the crisis in the United States medical system or the powers of discernment of the parrot: and despite the highly variable quality of the ideas on show, nobody was shouted down.

Despite this wealth of approaches to the problem of consciousness, all the speeches and all the bar-room conversations were really about one of two issues. Half concerned the notorious "hard problem" of the way in which experience of the physical world arises. The others were about everything else - the ins and outs of how we perceive, analyse and appreciate the world.

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However, many speakers at Tucson seem to think that the hard problem is either non-existent or at best not hard.

Patricia Churchland of the University of California pointed out that some problems in science that had been thought likely to be insoluble, such as finding out the composition of the stars, had proven surprisingly tractable. Others were attracted to the idea of Susan Greenfield of Oxford that the forming and reforming of patterns among our brains' billions of neurons is adequate to account for the complex information handling that consciousness implies.

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Closely related to the hard problem is the topic of "NCC", the neural correlate of consciousness. People hunting this elusive item think that there ought to be something detectable in the brain that confirms the presence of consciousness, and have proposed a clutch of candidates. Two people who think it is vital are Stuart Hameroff from Arizona, the conference's main organiser, and Roger Penrose from Oxford, who have worked together on the idea that consciousness arises from coherent quantum mechanical activity in the brain, and that a brain oscillation at 40 Hertz frequency is the manifestation of this coherent action.

But Professor Hameroff's Arizona colleague Alwyn Scott disagreed, saying that an analogy might be to look for the physiological correlates of human life. The heartbeat? The lungs pumping? The iron in your blood haemoglobin? Each is essential, along with many other characteristics, but life itself emerges from all of them without any magic ingredient.

Indeed, since humans have consciousness and we are a successful species, why not assume that consciousness has just developed by natural selection and that the hard problem was solved by Darwin?

The Tucson 3 conference in 1998 will probably hear a lot less about the hard problem and will be better for it. Once the subject became consciousness, not the reasons for consciousness, Tucson 2 became much more fun.

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Among the high points were a session on conscious machines which pitted Daniel Hillis, founder of the Thinking Machines company, against Jaron Lanier, a mathematician from Columbia University who also writes classical music and who played the piano at the openingceremony.

Asked whether machines can be conscious, Professor Hillis claimed that one that is large enough - say, the Internet, with millions of computers and pieces of software linked by billions of communications channels - just might.

Lanier said that they cannot - for example, the machine that recently won a game of chess against Gary Kasparov can play chess but do nothing else.

More importantly, Lanier said, even using the term degrades our own humanity and the way we think about ourselves. This view - that people and their consciousness are subjects that are best approached with a little awe and reverence - was one that almost everyone at Tuscon 2 seemed to have in common.

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